Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment

The LHCb collaboration

doi:10.1007/JHEP04(2026)170

Differential decay rate of B⁺→ J/ψK⁺ with the LHCb Upgrade I experiment

The LHCb collaboration

National Institute for Subatomic Physics
University of Warwick
University of Zurich
University of Liverpool
Syracuse University
University of Santiago de Compostela
University of Bristol
Department of Physics and Astronomy
Uppsala University
Université Paris-Saclay
University of Michigan, Ann Arbor
Université Clermont Auvergne
Faculty of Physics and Applied Computer Science
AGH University of Krakow
National Institute for Nuclear Physics
Fakultät Physik
TU Dortmund University
Vilnius University
CERN
University of Cambridge
Sorbonne Université
Universidade Federal do Rio de Janeiro
Peking University
University of A Coruna
NFN Sezione di Milano-Bicocca
University of Chinese Academy of Sciences
Consejo Nacional de Rectores (CONARE)
Institute for High Energy Physics
CPPM
Institute of Physics
Swiss Federal Institute of Technology Lausanne
Massachusetts Institute of Technology
Laboratoire Leprince-Ringuet
University of Oxford
Heidelberg University

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Resumen

The normalised decay rate of B⁺ → J/ψ(→ μ⁺μ⁻)K⁺ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb⁻¹ collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, A_FB, and the flatness parameter, F_H, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ⁺μ⁻ and b → dμ⁺μ⁻ transitions, which are particularly sensitive to physics beyond the Standard Model.

Idioma original	Inglés
Número de artículo	170
Publicación	Journal of High Energy Physics
Volumen	2026
N.º	4
DOI	https://doi.org/10.1007/JHEP04(2026)170
Estado	Publicada - abr 2026
Publicado de forma externa	Sí

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10.1007/JHEP04(2026)170

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title = "Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment",

abstract = "The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.",

keywords = "B Physics, Flavour Physics, Hadron-Hadron Scattering, Rare Decay",

author = "\{The LHCb collaboration\} and R. Aaij and Abdelmotteleb, \{A. S.W.\} and \{Abellan Beteta\}, C. and F. Abudin{\'e}n and T. Ackernley and Adefisoye, \{A. A.\} and B. Adeva and M. Adinolfi and P. Adlarson and C. Agapopoulou and Aidala, \{C. A.\} and Z. Ajaltouni and S. Akar and K. Akiba and M. Akthar and P. Albicocco and J. Albrecht and R. Aleksiejunas and F. Alessio and \{Alvarez Cartelle\}, P. and R. Amalric and S. Amato and Amey, \{J. L.\} and Y. Amhis and L. An and L. Anderlini and M. Andersson and P. Andreola and M. Andreotti and \{Andres Estrada\}, S. and A. Anelli and D. Ao and C. Arata and F. Archilli and Z. Areg and M. Argenton and \{Arguedas Cuendis\}, S. and L. Arnone and A. Artamonov and M. Artuso and E. Aslanides and \{Ata{\'i}de Da Silva\}, R. and M. Atzeni and B. Audurier and Authier, \{J. A.\} and D. Bacher and \{Bachiller Perea\}, I. and S. Bachmann and M. Bachmayer and \{Calderon Ramirez\}, S.",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2026.",

year = "2026",

month = apr,

doi = "10.1007/JHEP04(2026)170",

language = "Ingl{\'e}s",

volume = "2026",

journal = "Journal of High Energy Physics",

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AU - The LHCb collaboration

AU - Aaij, R.

AU - Abdelmotteleb, A. S.W.

AU - Abellan Beteta, C.

AU - Abudinén, F.

AU - Ackernley, T.

AU - Adefisoye, A. A.

AU - Adeva, B.

AU - Adinolfi, M.

AU - Adlarson, P.

AU - Agapopoulou, C.

AU - Aidala, C. A.

AU - Ajaltouni, Z.

AU - Akar, S.

AU - Akiba, K.

AU - Akthar, M.

AU - Albicocco, P.

AU - Albrecht, J.

AU - Aleksiejunas, R.

AU - Alessio, F.

AU - Alvarez Cartelle, P.

AU - Amalric, R.

AU - Amato, S.

AU - Amey, J. L.

AU - Amhis, Y.

AU - An, L.

AU - Anderlini, L.

AU - Andersson, M.

AU - Andreola, P.

AU - Andreotti, M.

AU - Andres Estrada, S.

AU - Anelli, A.

AU - Ao, D.

AU - Arata, C.

AU - Archilli, F.

AU - Areg, Z.

AU - Argenton, M.

AU - Arguedas Cuendis, S.

AU - Arnone, L.

AU - Artamonov, A.

AU - Artuso, M.

AU - Aslanides, E.

AU - Ataíde Da Silva, R.

AU - Atzeni, M.

AU - Audurier, B.

AU - Authier, J. A.

AU - Bacher, D.

AU - Bachiller Perea, I.

AU - Bachmann, S.

AU - Bachmayer, M.

AU - Calderon Ramirez, S.

PY - 2026/4

Y1 - 2026/4

N2 - The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.

AB - The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.

KW - B Physics

KW - Flavour Physics

KW - Hadron-Hadron Scattering

KW - Rare Decay

UR - https://www.scopus.com/pages/publications/105038107208

U2 - 10.1007/JHEP04(2026)170

DO - 10.1007/JHEP04(2026)170

M3 - Artículo

AN - SCOPUS:105038107208

SN - 1029-8479

VL - 2026

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

IS - 4

M1 - 170